1. Field of the Invention
The present invention relates to an anticorrosive agent capable of preventing a corrodible metal such as copper or the like from being corroded.
2. Description of the Related Art
In the process for producing a semiconductor device, a metal film of particular pattern is formed on a semiconductor wafer to form wirings and contact plugs. In such a step for formation of wirings and contact plugs, a corrosion inhibition technique is important in order to prevent the metal film from being corroded, for prevention of, for example, an increase in resistance. In recent years, copper, in particular, has come to be used widely as a material constituting the wirings and contact plugs, in order to make semiconductor devices operable at a high speed; therefore, the corrosion inhibitability requirement for the metal film has become stronger. It is because copper easily undergoes oxidation, etc. and tends to corrode although copper has such advantages as excellent electromigration resistance and low resistance.
As an example of the process in which corrosion inhibition for metal film is important, there can be mentioned a peeling step using a resist-stripper solution. When through holes are formed on metal wirings, a step is necessary which comprises forming holes by dry etching and then peeling and removing the residue of resist and the residue of etching. In this case, it is important to prevent the metal wirings from being corroded by the stripper solution used. Hence, it is widely conducted to allow the resist-stripper solution to contain an anticorrosive agent and thereby prevent the metal wirings from being corroded. As such an anticorrosive agent, there have heretofore been used aromatic hydroxy compounds such as catechol, pyrogallol, hydroxybenzoic acid and the like; carboxyl group-containing organic compounds such as acetic acid, citric acid, succinic acid and the like; and benztriazole (BTA) (e.g. JP-A-8-334905).
In the chemical mechanical polishing (CMP) conducted when the metal wirings are copper wirings, corrosion inhibition for copper is important not only for the prevention of quality deterioration of wiring copper due to corrosion but also for an operational reason. In the case of copper wirings, since fine processing by dry etching is difficult, patterning of wirings is ordinarily conducted by a so-called damascene process (FIG. 3). In the damascene process, first, wiring grooves are formed in an insulating film 3 [FIG. 3(a)], after which a barrier metal film 4 is formed on the whole surface of the resulting material. Then, thereon is formed a copper film 5 so as to fill the wiring grooves. Thereafter, chemical mechanical polishing (hereinafter referred to as CMP) is conducted to remove the copper film 5 at the areas other than the wiring grooves. Thus, copper wirings filled in the wiring grooves are formed. In CMP, since a corrosive slurry is used, copper corrosion easily proceeds; therefore, corrosion inhibition for copper becomes important. In CMP, there also arise other problems unique in CMP, such as (i) generation of dishing and erosion, (ii) generation of slit between copper film and barrier metal film and (iii) sticking of copper (polished by CMP) to polishing pad and wafer. To prevent these problems, corrosion inhibition for copper becomes important also. Description is made below on these problems.
Dishing refers to a phenomenon as shown in FIG. 4 that the surface of a copper film 5 is dented at the center. This is caused by a fact that the polishing rate of the copper film 5 is far larger than the polishing rate of a barrier metal film 4. Generation of dishing gives rise to various problems, for example, reduction in sectional area of wiring and resultant local increase in resistance.
Erosion refers to a phenomenon as shown in FIG. 3(c) that CMP proceeds excessively at a region of densely arranged wirings and the surface of the region is dented. Generation of erosion gives rise to an increase in wiring resistance and deteriorates the flatness of substrate surface, causing, for example, short-circuiting of wirings.
Slit between copper film and barrier metal film refers to a slit as shown in FIG. 4, generated by a kind of battery action during CMP. Generation of slit gives rise to an increase in wiring resistance and makes later film formation insufficient.
Sticking of copper (polished by CMP) to wafer, etc. refers to a phenomenon that copper ions generated during CMP accumulate on a polishing pad, then restick onto the wafer, whereby the flatness of wafer surface is deteriorated and short-circuiting is incurred. This problem is described in, for example, JP-A-10-116804.
Thus, corrosion inhibition for metal is necessary in CMP for prevention of the quality deterioration of wiring metal caused by corrosion and also for the operational reason. In conventional CMP, an anticorrosive agent has been used for the main reasons of prevention of dishing and prevention of sticking of copper to polishing pad, and benztriazole or a derivative thereof has been used (JP-A-8-83780 and JP-A-11-238709).
In the above, corrosion inhibition in production of semiconductor device has been stated. In other technical fields as well, various studies have been made on anticorrosive agents capable of appropriately preventing corrodible metals from being corroded. For example, JP-A-10-265979 discloses a technique of using BTA, etc. as an anticorrosive agent for preventing a copper material (e.g. copper wire or twisted copper wire) from being corroded.
As mentioned above, BTA and derivatives thereof all having relatively high corrosion inhibitability are in general use as an anticorrosive agent for corrodible metals (e.g. copper). BTA and derivatives thereof, however, have had a problem in that they are difficult to decompose by using biological organisms and the disposal of the waste liquid generated is difficult.
In recent years, the requirement for low environmental load has become increasingly strong and the safety requirement for waste liquid from plant has become higher. Waste liquids from plants are ordinarily decomposed by biological treatment (hereinafter referred to as xe2x80x9cbiodegradation treatmentxe2x80x9d). The above-mentioned BTA and derivatives thereof are difficult to subject to biodegradation treatment.
Therefore, in using an anticorrosive agent containing BTA or a derivative thereof, the waste liquid generated therefrom has inevitably been disposed by a method other than the biodegradation treatment, requiring a higher cost and more labor.
Meanwhile, in the field of resist-stripper solution, aromatic hydroxy compounds, carboxyl group-containing organic compounds, etc. have been used as an anticorrosive agent in some cases, as mentioned previously. These anticorrosive agents are generally superior in biodegradability to BTA and derivatives thereof; however, since they are intended for corrosion inhibition for mainly a wiring material made of an aluminum-copper alloy, they have no sufficient corrosion inhibitability for highly corrodible metals (e.g. copper) and have been difficult to use as an anticorrosive agent functioning under severe conditions such as CMP.
In view of the above situation, the present invention aims at providing an anticorrosive agent which has high corrosion inhibitability capable of effectively preventing a corrodible metal such as copper or the like from being corroded and also has good decomposability by biological organisms.
In developing an anticorrosive agent, how to allow the anticorrosive agent to have high corrosion inhibitability for metals has been an important technical task. In order to allow an anticorrosive agent to have biodegradability in addition to the corrosion inhibitability for metals, a study must be made from a standpoint different from conventional standpoints. The present inventors made a study from such a standpoint and found out that both high corrosion inhibitability and excellent biodegradability can be achieved by using an anticorrosive agent containing a combination of two kinds of compounds. The present invention has been completed based on the above finding.
According to the present invention, there is provided an anticorrosive agent containing, as essential components, (a) urea or an urea derivative and (b) a hydroxy aromatic compound.
According to the present invention, there is also provided an anticorrosive solution obtained by dissolving the above anticorrosive agent in water or an organic solvent.
According to the present invention, there is also provided an anticorrosive treating solution for corrosion inhibition treatment for a semiconductor wafer having the exposed surface of a metal film, which contains the above anticorrosive agent.
According to the present invention, there is also provided a preservative solution for storage of a semiconductor wafer having the exposed surface of a metal film, which contains the above anticorrosive agent.
According to the present invention, there is also provided a slurry for chemical mechanical polishing of the surface of a semiconductor wafer having the exposed surface of a metal film, which contains the above anticorrosive agent.
Hydroxy aromatic compounds have heretofore been used as an anticorrosive agent for aluminum alloy film in the field of resist-stripper solution. However, these hydroxy aromatic compounds show insufficient corrosion inhibition effect to corrodible metals such as copper when used by themselves. By using a hydroxy aromatic compound in combination with urea or an urea derivative, there is obtained an excellent corrosion inhibition action which is not obtainable only with either a hydroxy aromatic compound or urea or its derivative. There was a case (JP-A-11-21546) of using urea or an urea derivative as an oxidizing agent in the form of urea-hydrogen peroxide in, for example, a slurry for chemical mechanical polishing (hereinafter referred to as xe2x80x9cCMP slurryxe2x80x9d); however, there was no case of using as an anticorrosive agent. By combining a hydroxy aromatic compound with urea or an urea derivative, however, there is obtained a striking corrosion inhibition effect which has been unobtainable with conventional arts.
The reason therefor is not clear but is presumed to be as follows. A hydroxy aromatic compound is adsorbed on the surface of a metal (e.g. copper) film via the hydroxyl group or the like. At this time, the aromatic ring (which is hydrophobic) is at an exterior site; therefore, the metal surface becomes hydrophobic; as a result, copper is prevented from being corroded. Only with this hydroxy aromatic compound, however, it is difficult to cover all the metal surface sufficiently and densely. Meanwhile, urea or a urea derivative (hereinafter referred to as xe2x80x9curea type compoundxe2x80x9d as necessary) has, in the molecule, two nitrogen atoms showing an chelating action to a metal film and moreover has a relatively low molecular weight; therefore, is strongly adsorbed on the metal surface to form a dense coating layer. Moreover, since having high solubility in water, the urea type compound can be used in a large amount in an aqueous anticorrosive solution. Therefore, when a hydroxy aromatic compound and a urea type compound are used in combination, they act toward a metal film surface so as to supplement each other, and impart hydrophobicity to a metal surface and form a dense coating layer. As a result, an excellent corrosion inhibition action which has been unobtainable heretofore, can be obtained.
In addition, the anticorrosive agent of the present invention has very high biodegradability, and a waste liquid thereof can be disposed easily. Each urea type compound has a structure similar to those of urea, etc. (existing as a natural product in nature) and is very easily decomposed by biological organisms. Each hydroxy aromatic compound had good biodegradability as well. Therefore, the anticorrosive agent of the present invention has good biodegradability.